@ 9 lives: yes, "cheap" sounds unfortunate. The discussion will however be between two native speakers of Spanish, on both of whom this subtlety may well be lost. "Affordable" might sound less rough, though, indeed.
On the root of the matter: French clubs seem to rent out their 4-seater DR400's at around 100€, generally; while UK is a very different country, of course, why couldn't Spain be similar?